This invention relates generally to an exposure apparatus for manufacturing semiconductor circuit devices, and more particularly to a projection exposure apparatus having an arrangement for controlling the area of exposure.
Semiconductor devices such as integrated circuits (IC), large scaled integrated circuits (LSI) and very large scaled integrated circuits (VLSI) have been more and more densely integrated and their circuit patterns have been more and more miniaturized. Along these trends, the width of lines in the circuit pattern is required to be very fine to the extent of 1-1.5 microns. To achieve the higher integration of the semiconductor devices and the further miniaturization of the circuit patterns necessitates an exposure apparatus having an exposure performance capable of transferring or printing a fine pattern of the order of 1-1.5 microns line width and an alignment performance capable of precisely aligning the patterns through plural exposure steps with an alignment accuracy which is far higher than the exposure accuracy, while preventing occurrence of defects in the transferred pattern images.
In order to meet these requirements, there has already been developed an exposure apparatus of reduction projection type, called a stepper, wherein the image of an original, such as a reticle or mask, having formed thereon one or more circuit patterns is projected onto a recording member such as a wafer at a reduced scale, the projection exposure being repeated though a step-and-repeat process to reproduce a multiplicity of reticle patterns on the whole surface of the wafer.
While the pattern transfer itself is satisfactory according to the step-and-repeat type projection exposure system, there still remains another problem. The problem is that:
Usually, the region of the surface of the original or reticle other than the circuit pattern region is coated with a film of chromium or other material, by vacuum deposition or the like, in order to prevent the exposure light from being transmitted therethrough. If, however, the coating has defects such as pinholes or the coating is damaged for any reason, the exposure light transmits and leaks through such pinholes or damaged portion. The leaked light will be mixed into the pattern projection light at the current shot of exposure, or will be incident on the wafer area on which the circuit pattern has been projected or is to be projected at the preceding or succeeding shot of exposure. Thus, the leakage of exposure light results in serious defects in the printed circuit patterns and, therefore, is to be prevented.